forEach not matching in javascript

Question

So this should be relatively simple. In fact it should be super trivial. But I am blanking on how to handle this, consider the following method on a class:

  trigger(name, ...args) {
    let returnValue = null;

    if (!this.events.length > 0) {
      throw Error('There are no registered events.');
    }

    this.events.forEach((event) => {
      console.log(event.name, name)
      if (event.name === name) {
        if (args !== undefined) {
          returnValue = event.cb(...args, this);
        } else {
          returnValue = event.cb(this);
        }
      } else {
        throw Error('could not find ' + name + ' in the list of registered events.');
      }
    });

    return returnValue;
  }

Straight forward and simple. Heres the error:

console.log src/events/handler.js:51 event.with.params event.with.params

console.log src/events/handler.js:51 event.with.no.params event.with.params

It errors out if you have multiple events registered. I thought the easiest fix wad to do a return; once the name matches, as you can see it does match once. Heres the test:

  test('success in triggering multiple events', () => {
    eventHandler.register('event.with.params', (a, b) => {
      return a + ' ' + b;
    });

    eventHandler.register('event.with.no.params', () => {
      return 'no params'
    });

    expect(eventHandler.trigger('event.with.params', 'a', 'b')).toEqual('a b');
    expect(eventHandler.trigger('event.with.no.params')).toEqual('no params');
  });

Here you can see we register two events, then we attempt to trigger both of them. The error in the test is:

could not find event.with.params in the list of registered events.
    at Error (native)

Accept by console.log it did find it ... Then it continued on.

I know this is trivial to fix but I cant seem to figure it out. help ??

ps: if you use ...args, it will never be undefined unless your function was called as trigger(someName, undefined) - if trigger(someName) is called, args will be []. On a similar note,callback(...[], this) is the same as callback(this). — Mulan
– Mulan, Commented Apr 18, 2017 at 19:21
How do you handle the returnValue if multiple handler are registered for this event? At the moment you'll overwrite returnValue and return the value from the last callback called. — Thomas
– Thomas, Commented Apr 18, 2017 at 19:28
looks like your handler code will throw an error -if the first thing in events does not match the name- if there are any events registered with a different name, thanks @Thomas — thedude
– thedude, Commented Apr 18, 2017 at 19:29
@naomik, args will never be falsy. Even if called as trigger(someName, undefined) args will be [undefined] — Thomas
– Thomas, Commented Apr 18, 2017 at 19:29
@thedude, no it will throw if there is any event registered for a different name. — Thomas
– Thomas, Commented Apr 18, 2017 at 19:31

Yury Tarabanko · Accepted Answer · 2017-04-18 19:26:02Z

1

.forEach literally does it for each. So if you have ANY event with different name it will throw on it.

You could first filter events.

const filtered = this.events.filter(event => event.name === name);

Then check if there is any

if(!filtered.length) throw new Error(...)

Then run

filtered.forEach(event => /* run handlers */)

answered Apr 18, 2017 at 19:26

Yury Tarabanko

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